This invention relates to improvements in pneumatic wrenches of the type which include transmission means between the tool drive motor and the output spindle which is capable of changing the speed of the output spindle from a relatively high speed and low torque operating condition to a comparatively low speed and high torque operating condition. It is known in the art of pneumatic wrenches to provide mechanism for operation of the wrench to thread a fastener at relatively high speed during the so-called free rundown portion of the wrench operating cycle and then to also provide maximum driving torque during the final fastener tightening process. Such operation may be provided in tools having a single drive motor utilizing change speed transmission gearing together with suitable torque sensing mechanism to effect a shifting operation to decrease the output spindle speed and increase the torque output in response to a predetermined torque reaction in the drive mechanism of the wrench. U.S. Pat. No. 3,739,659 issued to William Workman, Jr. and assigned to Gardner-Denver Company discloses a speed shifting mechanism for a pneumatic wrench or nutsetter of the general type discussed hereinabove. The present invention is directed to improvements in torque responsive speed shifting mechanisms generally of the type disclosed in the above mentioned patent.
It is desirable to provide pneumatic wrenches or nutsetters which are adaptable for use as single spindle units either hand held or base mounted or as a multiple unit arrangements for tightening a plurality of fasteners generally simultaneously. In many plural fastener joining operations it is desirable to commence the final torquing of all fasteners at the same time or in a predetermined sequence. Accordingly, a wrench shifting mechanism which is suitable for single wrench units as well as multiple spindle arrangements should be capable of being controlled to shift automatically at a predetermined torque reaction in the tool drive means or to shift in response to an external signal so that simultaneous shifting or predetermined sequence shifting of all spindles in a multiple wrench may be obtained.